A golf ball including a unitary core having a volume, an outer surface, a geometric center, and an outermost transition volume adjacent to the outer surface, the core being formed from a substantially homogenous composition; and a cover layer including ionomer, metallocene-catalyzed polymer, polyester, polyamide, non-ionomeric thermoplastic elastomer, copolyether-ester, copolyether-amide, polycarbonate, polybutadiene, polyisoprene, or polystyrene block copolymer. The outermost transition volume is disposed between the core outer surface and the geometric center, the transition volume has an outer portion congruent with the core outer surface, and comprises the outermost 45% of the core volume or less. Both a hardness of the core outer surface and a hardness within the outermost transition volume are less than the hardness of the geometric center to define a negative hardness gradient.